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Thanks to decomposers such as bacteria and earthworms, soil is always changing. Organic matter goes from recognizable to indistinguishable due to the constant work of processing carried out by these organisms. If it weren't for them, soil would be a static environment in which nothing would grow, a situation that would seriously impact every other life form on the planet.

How Soil is Made

Soil doesn't just happen. It is the result of hundreds of years of activity that takes place above and beneath its surface. The primary work of decomposition is done by earthworms and bacteria that eat dead vegetation, transforming it into the rich, dark substance known as humus. The process is relatively simple and straightforward. Decomposers consume the materials, digest them and then eliminate them back into the soil in an entirely different form. While bacterial function differs among the species, they all share the common outcome of making organic materials more accessible to plants. Earthworms function in a similar way, by consuming actual dirt particles along with certain types of vegetation with the result of breaking them down into smaller sizes that plants can use.

Earthworm Action

Common earthworms (Lumbricus terrestris) are classified as invertebrates due to their lack of a skeletal system. Their segmented bodies typically grow to about 3 inches long, although some have been known to grow to 14 inches. Their sole purposes in life are tunneling into the soil, digesting it as they go along, and procreating to produce more of their kind. Earthworms that act as decomposers may be one of three species. Epigeic worms live in plant litter, making them ideal for processing compost. Endogeic worms live in the upper layer of soil and feed mainly on organic matter. Anecic worms, exemplified by the night crawler, burrows deeply into the soil, transporting vegetation into its tunnels.

Bacterial Action

Bacteria are so tiny that between 100 million to 1 billion of them can live in a single teaspoon of fertile soil. As decomposers of plant materials, they function by consuming and processing plant materials and retaining the nutrients in their cells. Bacteria also work in conjunction with plants to produce, or fix, nitrogen, a nutrient that is important to many vegetables including legumes. Another important group of bacteria, called actinomycetes, produce the familiar earthy smell of freshly tilled soil. They process substances that other bacteria have difficulty decomposing, such as plant cellulose and chitin, a hard substance that lines the cell walls of fungi.

Benefits

Along with dirt, earthworms consume pieces of vegetation left behind by dying plants. In the process, their digestive systems extract nutrients that they return to the soil in the form of castings. In addition to this benefit, the tunnels they dig as they move through the soil aerate it by providing passageways through which air and water can move more efficiently. Bacteria work to further break down what earthworms may leave behind, and also improve water filtration and aeration by helping to bind its particles together.

About the Author

Rachel Lovejoy has been writing professionally since 1990 and currently writes a weekly column entitled "From the Urban Wilderness" for the Journal Tribune in Biddeford, Maine, as well as short novellas for Amazon Kindle. Lovejoy graduated from the University of Southern Maine in 1996 with a Bachelor of Arts in English.